Rainfall Shortage Sequence 04/2019

Sequence of raiinfall shortages to April 2019

By April 2019, driest-ever rainfall totals occur at durations of 15, 18, 24 and 30 months. The total for 12 months is the second driest for that duration.

This contour plot shows the progress of the drought at Manilla up to April 2019. Colours show rainfall shortages as percentiles. Dates plot along the top, and durations down the side.

One month rainfall totals (on the top row)

April 2019, which had no rain, followed eight months without serious monthly rainfall shortages. Months of serious rainfall shortage (light brown) had come earlier, in May, June and July 2018, and also in September 2017.

Shortages lasting less than one year (rows 2 to 9)

As the effects of low monthly rainfall added up, extreme shortages appeared (dark brown). That is, rainfall totals in the lowest 1% of the historical record.
By June 2018, the 2-month and 3-month totals were already extreme shortages. Similarly, by July, the 3-month, 4-month, and 5-month totals were all extreme shortages. By September 2018, extreme shortages extended as far as 9-month totals. That total, adding up the nine months from January to September 2018, included only one month (February) that had rainfall above normal.
In these shorter durations, extreme shortages were rare after September 2018. March 2019 included no shortages (not even “serious” ones) for durations from 2 months up to 6 months. However, April saw some serious shortages return.

Shortages of 1-year to 3-year duration (rows 12 to 36)

By August 2018, an extreme 15-month shortage appeared. The 15-month total then included not only the dry months of winter 2018, but also the dry month of September 2017. By September 2018, the 15-month total became the driest on record (400 mm). By October four totals in this group (12-, 15-, 18-, and 24-month totals) were extreme shortages. That was true again in January 2019. By that time, some dry months in 2017 were excluded, but dry months in the current summer were included.
In February 2019, as the four extreme shortages of the previous month persisted, the 12-month total became the driest ever (271 mm). March also had four extreme shortages in this group, but now they were at 12, 15, 24 and 30 months. The 24-month total (769 mm) was the second-driest on record and the 30-month total (1078 mm) equal driest.
April was much worse: lowest-ever or second-lowest values appeared for all five durations from 12 months to 30 months.

The 2002 extreme drought

Contour chart 2002 drought at Manilla NSWA similar graph was posted in “The 2002 drought contour chart”. It is clear that, in that case, extreme shortages did not extend through the 15- to 30-month durations that have the most extreme shortages now.

A line graph for April 2019

A profile of the rainfall status for April 2019 reveals that extreme shortages also exist at durations much longer than shown in this contour graph: durations of six years and seven years. Severe shortages even occur at durations of ten years and twenty years.


Data and method

This kind of graph simply displays the time sequence, month by month, of rainfall shortages that I have displayed on line graphs prepared for each month. In the post for the most recent line graph (April 2019) I have described my method of analysis and its limitations.

Rainfall Shortage Jan 2000 – Mar 2019

Severe and extreme rainfall shortages Jan 2000 to Mar 2019

The current drought now has an extreme rainfall shortage of 84 months duration that must have commenced in 2012.

A new graph

This graph shows the onset, persistence, and breaking of episodes of extreme and severe rainfall shortage (droughts) at Manilla since 2000. It is a part of a graph of the complete historical record from 1884. In this case, the time axis is expanded to resolve individual months.

Complete record severe and extreme rainfall shortagesThe features of this “onset-to-breaking” kind of graph and the data analysis are explained in the post “Rainfall Shortage History: Manilla”.

Extreme shortages, up to the 1st percentile, are shown in red and severe shortages, up to the 5th percentile, are shown in grey.
The dashed line labelled “Last Good Data” is a limitation to determining cumulative rainfall deficiency. Future observations may make any point to the right of this line more extreme.

The pattern of rainfall shortages from 2000

Shortages before 2018

In 2000 there were no rainfall shortages classed as “severe”. There had been hardly any since 1994.
The drought that occurred in winter 2002 had extreme rainfall shortages at all durations from 3 months to 12 months. Severe shortages extended even further: from 2 months to 30 months. However this was a much shorter drought than six others in the history of Manilla.

Although severe rainfall shortages (grey) occurred at intervals between 2002 and 2018, they formed small clusters, mainly at short durations. Years affected were 2005, 2008, 2009, 2012, 2013, 2014, and 2017. By 2014, there was public concern about shortage of rainfall. Although there were few seasonal severe shortages at that time, the graph shows that there were severe shortages at durations from 12 months to 30 months through 2013 and 2014.

With the benefit of current data, we can see that severe and even extreme shortages of duration longer than 60 months were, in fact, initiated in 2012 or earlier. They were not apparent at the time, however. In October 2016, in a post “Is There Any Drought Now?”, I argued that there was no evidence of drought at that time.

An alternative expression of rainfall status during this time is a graph of smoothed rainfall anomalies in the post “17 Years of “Droughts and Flooding Rains” at Manilla”.

Shortages at 2018

Shortages of rainfall became alarming in 2018. The winter months had extreme shortages of 2-month to 6-month duration. Earlier and later dry months contributed to a 15-month extreme shortage, such as had not occurred since 1966, half a century earlier.
After November 2018 none of the short-term rainfall totals for durations less than nine months has been even a severe shortage. In other respects, the drought has deepened. As recent monthly rainfall values have scarcely risen above normal, durations of severe or extreme shortage have become longer and longer. As at March 2019, extreme shortages prevail at 30 months, 72 months and 84 months. Severe shortages prevail at even longer durations, now up to 120 months (10 years).

Other Current Graphs

Other graphs of the drought, current to March 2019 data, are in two posts: “March Rain Leaves Drought Extreme”, and “Rainfall Shortage Sequence 03/2019”.


Notes

The Millennium Drought absent
“Rainfall Shortages” or “Droughts”?
Short droughts are worst

The Millennium Drought absent

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Rainfall Shortage History: Manilla

Complete record of droughts, Manilla NSW

Manilla had great droughts in 1902, 1912, 1940, 1946, 1966, and 2018.

A new graph

This new graph records all historic periods of severe and extreme rainfall shortage at Manilla NSW. Data show 25 values of duration from 2 months to 360 months. Unlike the graphs of rainfall shortage in earlier posts, this graph shows the months of onset, persistence, and breaking of each occurrence. [See the Note below: “An innovative graph”.]
Extreme shortages (up to the 1st percentile) are shown in red and severe shortages (up to the 5th percentile) are shown in grey.
The dashed lines labelled “First Good Data” and “Last Good Data” are limitations that apply to all cumulative rainfall deficiency data. [See the note below: “First Good Data; Last Good Data”.]

“Rainfall Shortages” or “Droughts”?

Although droughts involve other factors, rainfall shortage is decisive. Some other factors, such as daily maximum temperature anomaly, vary in the same sense, Australia-wide.
Recognised times of drought at Manilla appear on this graph as extended periods of severe or extreme rainfall shortage .
To simplify, I have separated the graph into three parts according to the duration of the shortages: seasonal droughts, great droughts, and decadal droughts.

Complete record of seasonal droughts

Seasonal droughts.

Droughts with extreme shortages of rainfall that lasted up to nine months happened often. Counting those with more than one red marker, there were 16 seasonal droughts in 136 years: about one in each nine years. Gaps as short as four years happened around 1920, while the longest gap of 16 years came between 2002 and 2018.
The most common season of extreme rainfall shortage was winter, with 8 cases. Autumn had 5 cases and spring 3 cases, while summer had none.
Some of these seasonal droughts became Great Droughts.

Complete record of the great droughts

The Six Great Droughts: 1-year to 9-year duration.

According to this graph, Manilla has suffered six great droughts, attested by extreme shortages of rainfall at more than 2 of the 13 chosen duration values from 12 months to 108 months. They were:

(1.) 1902 (the Federation Drought);
(2.) 1912;
(3.) 1940 (first part of the World War II Drought);
(4.) 1946 (second part of the World War II Drought);
(5.) 1966;
(6.) 2018.

[The absence of the Millennium Drought is discussed in the Note below.]

BoM continental rainfall maps

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Rainfall Shortage Sequence 03/2019

Sequence of raiinfall shortages to March 2019

By March 2019, extreme shortages of rainfall occur at durations from 12 months to 30 months.

This contour plot shows the progress of the drought at Manilla up to March 2019. Colours show rainfall shortages as percentiles. Dates plot along the top, and durations down the side.

One month rainfall totals (on the top row)

By March 2019, there had been eight months without serious monthly rainfall shortages. The months of serious rainfall shortage (light brown) were earlier, in May, June and July 2018. The only other month in the last two years with such low rainfall was September 2017.

Shortages lasting less than one year (rows 2 to 9)

As the effects of low monthly rainfall added up, extreme shortages appeared (dark brown). That is, rainfall totals in the lowest 1% of the historical record.
By June 2018, the 2-month and 3-month totals were already extreme shortages. Similarly, by July, the 3-month, 4-month, and 5-month totals were all extreme shortages. By September 2018, extreme shortages extended as far as 9-month totals. That total, adding up the nine months from January to September 2018, included only one month (February) that had rainfall above normal.
In these shorter durations, extreme shortages were rare after September 2018. The final month plotted (March) includes no shortages (not even “serious” ones) for durations from 2 months up to 6 months.

Shortages of 1-year to 3-year duration (rows 12 to 36)

By August 2018, an extreme 15-month shortage appeared. The 15-month total then included not only the dry months of winter 2018, but also the dry month of September 2017. By September 2018, the 15-month total became the driest on record (400 mm). By October four totals in this group (12-, 15-, 18-, and 24-month totals) were extreme shortages. That was true again in January 2019. By that time, some dry months in 2017 were excluded, but dry months in the 2018-19 summer were included.
In February 2019, as the four extreme shortages of the previous month persisted, the 12-month total became the driest on record (271 mm). March also had four extreme shortages in this group, but now they were at 12, 15, 24 and 30 months. The 24-month total (769 mm) was the second-driest on record and the 30-month total (1078 mm) equal driest.

A related graph

A line graph of the rainfall status for March 2019  extends to durations much longer than the 36 months shown in this contour graph. It reveals that extreme shortages exist at durations of six years and seven years.


Data and method

This kind of graph simply displays the time sequence, month by month, of rainfall shortages that I have displayed on line graphs prepared for each month. In the post for the most recent line graph (March 2019) I have described my method of analysis and its limitations.

One- and two-year droughts recur in January 2019

Drought contour plot to Jan 2019

This contour plot shows the progress of the extreme drought at Manilla up to January 2019. Colours show rainfall shortages as percentiles. Dates plot along the top, and durations down the side.

One month rainfall totals (on the top row)

By January 2019, there had been six months without serious monthly rainfall shortages. The months of serious rainfall shortage (light brown) were earlier, in May, June and July 2018. The only other month with such low rainfall was September 2017.

Droughts lasting less than one year (rows 2, 3, 4, 5, 6, 9)

As the effects of low monthly rainfall added up, extreme droughts appeared (dark brown). That is, rainfall totals below the 1st percentile. (They are the lowest rainfall totals, that have occurred in less than 1% of the historical record.)
By June 2018, the 2-month and 3-month totals were already extreme shortages. Similarly, by July, the 3-month, 4-month, and 5-month totals were extreme shortages. By September 2018, extreme shortages extended as far as the 9-month total. That total, adding up the nine months from January to September 2018, included only one month (February) that had rainfall above normal.
In these durations of less than one year, extreme droughts were rare after September 2018. Because the last six months had no serious monthly shortages, the final month (January) includes no serious shortages for durations from 2 months up to 6 months.

Droughts of 1 year to 2 year duration (rows 12, 15, 18, 24)

By August 2018, an extreme 15-month drought appeared. That 15-month total then included not only the dry months of winter 2018, but also the dry month of September 2017. By September 2018, the 15-month total became the driest on record (400 mm). By October all four droughts in this group (12-, 15-, 18-, and 24-month droughts) were extreme. This became true again in January 2019. By that date, some of the dry months of 2017 were no longer included, but dry months in the current summer replaced them in the total.


Related graphs

A similar contour plot with data to October 2018 is here.

A line graph of the rainfall status for January 2019 reveals that extreme shortages also exist now at the much longer durations of six years and seven years that are not included in this contour plot.


Notes

The following notes include:

Classes of rainfall shortage

Rainfall rate versus percentile rank

Limitations of this analysis

Note: Classes of rainfall shortage

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The 2002 drought contour chart

Contour chart 2002 drought at Manilla NSW

The 2002 drought at Manilla was a failure of winter rainfall. [See Note below: “Manilla’s rainfall seasonality”.]

The top line of this contour chart shows that monthly rainfall shortages occurred in all the six months of winter rainfall dominance (April to September) of 2002. Shortages in May and July were severe, below the 5th percentile. In the summer rainfall months (October to March) that preceded and followed, rainfall was near or above normal. [See Note below: “Classes of rainfall shortage”.]

Lower down the contour chart, rainfall shortages of longer duration are shown. For droughts of 3 months duration, the rainfall shortage was extreme (1st percentile) by July 2002, as it included the serious shortage of May as well as that of July. In the same way, one sees extreme 6-month shortages in September and October, as all the monthly rainfall shortages since March added up.

By November 2002, one sees extreme droughts of 9 months and 12 months duration. The 9-month drought incorporated the consecutive months of below-normal rainfall from March to November. The extreme 12-month drought (307 mm) that was evident in November 2002 began earlier, with below-normal rainfalls in December 2001 and January 2002. That was the fourth driest 12-month period on record, after October 1965 (288 mm), August 1946 (302 mm) and November 1965 (304 mm).

The 2002 drought had no extreme rainfall shortages longer than 12 months. There were, however, some severe shortages of 18 months duration and some serious shortages of 24 months duration, due to some low rainfalls in the previous winter (2001).

By April 2003, hardly any serious rainfall shortages due to the 2002 drought remained. [See Note below: “Limitations of this analysis”]

More about the 2002 drought

Graph of monthly percentile rainfall in a droughtAnother approach to describing this 2002 drought is in the post “The 2002 rainfall shortages at Manilla”. That post has a graph showing selected monthly profiles of percentile values. It also links to two earlier posts with graphs of smoothed values of climatic anomalies.

The 2018 Drought

Drought 2018 contour chartA similar contour plot for the drought of 2018 reveals similarities and differences.


Note: Classes of rainfall shortage

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Contours of Manilla’s 2018 Drought

Drought 2018 contour chart

Displaying drought severity, date, and duration.

This image shows how an extreme drought developed at Manilla, NSW in 2018. The contours and colours indicate drought severity. They show whether the rainfall shortage was extreme, severe, or merely serious. At times without drought, they show when the rainfall was above normal.
[See Note below: “Classes of rainfall shortage”.]
Calendar months appear in order along the top, showing how the severity of drought has changed as time has passed.
Down the side, the duration of drought is shown, from one month duration at the top to thirty-six months duration at the bottom. Each month is shown on one vertical line, with a severity value plotted against each duration value.
[In other posts (like “Record 15-month Drought in 2018”) each individual month’s drought data is plotted as severity versus duration.]

The pattern of the 2018 drought

Development

In each of the months May, June, and July 2018, the monthly rainfall was a serious or severe shortage, below the 10th percentile. As rainfall had been below normal also in March and April, each month after April saw severe and even extreme shortages that extended to durations of 3 months and longer. By August, there were extreme droughts of five-month and six-month duration, despite reasonable rain (28 mm) having fallen in August.
By September, the nine months to date were in extreme drought. That is to say, the first nine months of 2018 had a total rainfall lower than any but 1% of all nine-month periods in history.
However, in that month (September 2018), the rainfall shortage for a 12-month duration was not extreme, but merely severe. Yet the 15-month shortage for that month was also extreme. In fact, it was the lowest 15-month rainfall total in history (400 mm).
The source of the extreme 15-month shortage at this date is obvious. One year earlier, the month of September 2017 had a serious rainfall shortage, and the two previous months had little rain. From these short-term shortages in spring 2017, shortages of longer duration descend as an arc across the graph. They become mild nine-month shortages during the summer, then worsen to extreme by merging with 2018 shortages.

Seasonality

Manilla’s rainfall is seasonal, with two distinct modes, each dominating half the year. There is a major summer (monsoonal) mode and a minor winter (westerly) mode. The summer rainfall mode dominates from October to March and the winter rainfall mode dominates from April to September. [See Note below: “Manilla’s rainfall seasonality”.]
This graph documents a failure of winter rainfall. The 2018 months that had rainfall shortages were the months of dominance of the winter rainfall mode (April to September). Rainfall had been near or above normal in the preceding summer rainfall mode (October 2017 to March 2018), and was so again in October 2018. [See Note below: “Limitations of this analysis”]
The rainfall shortages in the previous year (2017) were also restricted to the months of the winter rainfall mode, but began very late. Shortages did not develop until the final three months (July, August, September). Only when the extreme drought of 2018 developed did those 2017 shortages have a big effect.


The 2002 drought contour plot

Contour chart 2002 drought at Manilla NSWThe most recent extreme drought at Manilla before 2018 was the drought of 2002.
A contour plot in the same format is in this post.


Note: Classes of rainfall shortage

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